1. Field
The present disclosure relates generally determining timing in a wireless communication system and, more specifically to apparatus and methods for determining timing in order to resolve timing ambiguity in a transceiver of a wireless communication system, which thereby effectively extends the timing tracking dynamic range.
2. Background
In certain wireless communication systems, such as a system employing orthogonal frequency division multiplexing (OFDM) as an example, timing tracking of transmitted signal is performed based on channel estimation. A signal channel is commonly estimated using pilot signals, which are transmitted as part of the total signal. The length of channel estimation is limited by the number of pilot channels transmitted, which is limited by the overhead cost resulting from pilot channel transmission. In one example of an OFDM system, a maximum number of two FDM pilot channels are used to limit the overhead due to transmission of the pilot channels. In such an example, the maximum length of channel estimation for timing tracking would be limited to an “L” number of samples, where L=1024 samples or chips. Assuming in such a system that the actual maximum channel length is 768 samples or chips, the dynamic range left for timing tracking is very limited (i.e., 256 samples or chips). Accordingly, in such applications as this where the channel estimation is not sufficiently longer than the actual channel length (i.e., 1024 is not much greater than 768), currently known timing tracking becomes problematic since the dynamic range of timing is limited (i.e., ±128 samples or chips).
Furthermore, due to the periodicity (i.e., the characteristic or quality of occurring at regular intervals) of channel estimation, further ambiguity in the timing tacking may result. Because of periodic nature of channel estimation, early appearing signal symbol energy of a specific channel resulting from multipath transmission of the signal will actually appear “late” in the channel estimate because of “wrap around.” Similarly, late appearing signal symbol energy will actually appear as early in the channel estimate. Thus, timing ambiguity can result since early or late appearing symbol energy in the channel estimate may actually be the converse.